Method of making double-oriented single crystal castings

ABSTRACT

A method by which to produce single crystal parts in which the orientation of the dendrite growth in two planes at right angles to one another is described. In effect this produces an orientation in all three right angle planes of the cast article.

I United States Patent 1 1 1 1 3,738,416 Kear et al. June 12, 1973 METHOD OF MAKING DOUBLE-ORIENTED [56] References Cited SINGLE CRYSTAL CASTINGS UNITED ST PATENTS [75] Inventors: Bernard H. Kear, Madison, Conn.; 3,572,419 3/1971 Barrow eta]. 164/60 Larry W. Sink, Milwaukee, Oreg. 3,519,063 7/1970 Piearcey 3 342,455 9 1967 F] k t l. [73] Assignee: United Aircraft Corporation, E 2:791,813 541957 Dzl ancij Hartford, Conn- 3,580,324 5/1971 Copley et a] 164/60 [22] Filed: Feb. 1, 1971 Primary ExaminerJ. Spencer Overholser [21] Appl' 111,638 Assistant Examiner-John E. Roethel Related US. Application Data Attorney-Charles Warren [62] Division of Ser. No. 806,869, March 13, 1969, Pat.

No. 3,598,176. [57] ABSTRACT A method by which to produce single crystal parts in [2%] w t/61321163933; which the Orientation of the dendrite growth in two E g 122 125 planes at right angles to one another is described. In effect this produces an orientation in all three right angle planes of the cast article.

3 Claims, 4 Drawing Figures METHOD OF MAKING DOUBLE-ORIENTED SINGLE CRYSTAL CASTINGS This is a division of application Ser. No. 806,869, filed Mar. 13, 1969, now Pat. No. 3,598,176

BACKGROUND OF THE INVENTION The copending application of Piearcey, Ser. No. 540,114, now U.S. Pat. No. 3,494,709 assigned to the same assignee as this application, describes the casting of single crystal parts in which the dendrite growth is oriented with respect to the longitudinal axis of the cast part. However, for certain devices, a more precise orientation of the dendrites in a plane at right angles to the longitudinal axis may be essential and may produce, in some particularly stressed parts a superior strength, since the strength of the single cyrstal castings varies in accordance with the orientation of the dendrites.

SUMMARY OF INVENTION One feature of the invention is a method by which orientation of crystals in both vertical and horizontal direction may be obtained.

A principal object of the invention is the production of single crystal castings in which the crystalline orientation, the dendrite growth is selectively oriented in each of two directions at right angles to one another.

In accordance with the invention, the casting is made in a mold having associated therewith a pair of chill plate surfaces at right angles to one another to establish columnar grain growth perpendicularly to each chill surface. The inter-secting grain growths produce a vertical grain growth in which the dendritic growth is positioned at right angles to both chill surfaces and thus doubly oriented. From this'doubly oriented growth a single crystal is selected to grow into the effective mold portion.

Other features and advantages will be apparent from the specification and claims, and from the accompanying drawings which illustrate an embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view through a device embodying the invention.

FIG. 2 is a transverse sectional view along line 22 of FIG. 1.

FIG. 3 is a greatly enlarged diagrammatic view of a vertical section of a doubly-oriented single crystal castmg.

FIG. 4 is an enlarged diagrammatic view of a horizontal section of the same single crystal casting.

DESCRIPTION OF THE PREFERRED EMBODIMENT The double oriented casting is made in a ceramic tube mounted ona box 12 constituting a chill. The latter has a cooled bottom surface 14, and cooled side surfaces 16 and 18 at right angles to one another and at right angles to the bottom surface. These surfaces are the inner surfaces ofa bottom wall 20 and side walls 22 and 24 all of which are cooled by cooling coils. 26 embedded therein or in contact with the outer surfaces. The tube 10 has a flange 28 adjacent but spaced from the lower end and this flange serves to support the tube on the box l2.

The tube is surrounded by a plurality of axially aligned heating coils 30, preferably induction heating coils, and these maybe separately controlled for establishing the desired temperature gradient in the tube as described in the Lyons U.S. Pat. No. 3,346,039. Within the tube 10 are secured individual article molds 32 and 34 in which the doubly oriented articles are cast. Each mold has a restricted opening 36 at the bottom which is of a size to permit the entry of a single crystal of the plurality of columnar grains growing in the tube, as will be later described.

In use, the tube 10 and the molds therein are heated by the surrounding coils to a temperature above the melting point of the alloy to be cast. Water is then circulated through the cooling coils for the chill plate and the alloy is poured into the tube. As the alloy fills the box 12 and the tube 10 it also fills the molds 32 and 34 but is kept molten within the tube and molds by reason of the temperature of these parts.

Crystallization begins at the chill plate as soon as the alloy comes in contact with the chill surfaces and directional solidification begins with the columnar structure perpendicular to each chill surface as described in a VerSnyder U.S. Pat. No. 3,260,505. The dendritic growth in these columns is also at right angles to the chill surfaces from which the columnar growth extends so that dendritic growth is oriented in directions at right angles to'each of the several chill surfaces. The downwardly extending lower end of the tube 10 serves as a baffle to prevent misoriented grains which may nucleate from the top of the chill from entering the inside of the tube.

The grains from the side chill surfaces and the grains from the bottom surface intersect and cause vertical heat flow through the horizontally oriented columnar grains and, with the resultant fast vertical cooling a doubly oriented close columnar grain structure then grows upward within the tube toward the molds. This fast vertical cooling is faster than the columnar growth in either horizontal or vertical direction in the'box 12 because, as soon as the columnar growth begins in a vertical direction within the tube, all of the cooling effect of both the vertical chills and the horizontal chill is used in heat removal from the solidifying material within the tube. Thus, the grain growth of dendritic growth within the tube has its principal growth in a vertical direction within the tube and this is the direction of the greatest strength in the cast article. The small opening in the bottom of each mold selects a single doubly oriented grain to grow in each mold, the single grain functioning in effect as a single seed crystal. By close control the temperature gradient within the tube, the solidification of the alloy in the tube and in the mold will occur at such a rate as to produce single crystal parts in each mold.

Other shapes of chill cavities may be used and an orientation of the chill surfaces differently with respect to the longitudinal axis of the tube may serve to control the orientation of the crystalline structure within each mold. Thus, if the tube extends at an acute angle to the horizontal chill surface the dendrites will have the same acute angle in the crystal in each mold.

Where the mold has a small opening at the lower end, as above described, it will be apparent that the mold may be relatively large with respect to the tube as the mold will fill from the top as soon as the tube is filled to a point above the top of the mold. The control of the temperature gradient within the tube by controlling the energy supply to the several coils, thereby to produce the desired fast solidification rate from the bottom to the top of the tube with the liquid-solid interface remaining basically horizontal during the solidification, is well known as described, for example, in VerSnyder US. Pat. No. 3,260,505 or Lyons US. Pat. No. 3,346,039.

We claim:

1. The method of casting in a mold a single crystal, doubly-oriented article from an alloy, the method including the steps of:

providing a container to receive the alloy,

positioning the mold within a tube with an open lower end of the mold adjacent the lower open end establishing columnar growth in the alloy in the container, said columnar growth being in two directions at right angles to one another to produce co lumnar grains in said two directions, causing an upward columnar growth from the alloy container in the alloy tube to cause doublyoriented columnar grains to grow therein, and selecting one of said grains to grow into the mold through said open lower end as doubly-oriented single crystal. '2. The method of casting as in claim 1 in which the columanr growth is established by chill plates at right angles to one another, with the further step of:

providing a constriction at the end of the mold adjacent the chill plate by which to promote single crystal growth within the mold. 3. The method of casting as in claim 1 with the added step of:

providing a restriction at the end of the mold adjacent the start of the columnar growth to select a single grain to grow within the mold. 

1. The method of casting in a mold a single crystal, doublyoriented article from an alloy, the method including the steps of: providing a container to receive the alloy, positIoning the mold within a tube with an open lower end of the mold adjacent the lower open end of the tube, positioning the mold and tube above the container in a substantially vertical position with the bottom end of the tube below the top of the container, filling the container with the alloy so that a bottom end of the tube is immersed in the alloy and also filling the mold and tube with the alloy, establishing columnar growth in the alloy in the container, said columnar growth being in two directions at right angles to one another to produce columnar grains in said two directions, causing an upward columnar growth from the alloy container in the alloy tube to cause doubly-oriented columnar grains to grow therein, and selecting one of said grains to grow into the mold through said open lower end as doubly-oriented single crystal.
 2. The method of casting as in claim 1 in which the columanr growth is established by chill plates at right angles to one another, with the further step of: providing a constriction at the end of the mold adjacent the chill plate by which to promote single crystal growth within the mold.
 3. The method of casting as in claim 1 with the added step of: providing a restriction at the end of the mold adjacent the start of the columnar growth to select a single grain to grow within the mold. 